In recent years, portable terminal apparatuses have functionally evolved in terms of high-quality video reproduction, large-screen displays and multi-application compatibility, for example. Along with the development of high-function portable terminal apparatuses, it has become important to consider how to perform process for compositing and displaying drawings in a plurality of applications in a power saving manner.
As a conventional technique for compositing screens in which a plurality of display frames (i.e., display layers) including a moving image are composited, a technique disclosed in Patent Literature (PTL) 1 is known. The technique of PTL1 produces a video frame, background frame, and a foreground frame separately. In the technique disclosed in PTL 1, an on-screen image is produced by sequentially superimposing the background frame, the video frame, and the foreground frame in a predetermined order. The “video frame” is configured with display layers for displaying a video image (i.e., moving image). The “background frame” is configured with display layers for displaying a background image (i.e., still image) positioned at the back (lower-layer side) of the video frame. The foreground frame is configured with display layers for displaying a front image (i.e., still image) positioned at the front (upper-layer side) of the video frame. In other words, the technology in PTL 1 discloses that the display layers positioned at the back frame side with respect to the video frame are pre-composited before compositing the background frame with the video frame. Moreover, the technology in PTL 1 discloses that the display layers positioned at the front frame side with respect to the video frame are pre-composited to produce the foreground frame.
The background frames (still image) and the foreground frames (still imago) are updated less frequently than the video frame image (moving image). In other words, in the above-described conventional technology, there is no need to update the background frame and the foreground frame simultaneously with an update of the moving image frame. Accordingly, the screen compositing apparatus in the above-described technique may composite the three frames: the background frame, the moving image frame and the foreground frame immediately before final screen output. Thus, the above-described conventional technology enables power saving by reducing a process load when producing an on-screen image.